The traditional tools for detecting and diagnosing renal masses are tomographic imaging, including ultrasound, CT, and MRI. Currently, these real-time detection tools play a very important role in the diagnosis and management of patients with kidney disease. In fact, most renal masses can be correctly diagnosed by a single imaging study. For example, benign masses such as simple renal cysts, infectious diseases (e.g., focal bacterial pyelonephritis) and vascular smooth muscle lipomas can be correctly diagnosed based on typical imaging and clinical information.
Although some benign and malignant cystic renal masses have many similarities, the imaging expert can identify most benign and malignant tumors based on specific imaging features. As long as the mass has the imaging features of a malignant tumor, it can be surgically resected in most patients without the need for a preoperative biopsy as long as the tumor can be surgically removed. In other words, the positive predictive value of imaging findings is so high that even a negative biopsy result will not change the management plan. However, some renal masses cannot be correctly diagnosed with confidence from imaging findings alone, and percutaneous renal biopsy used to play a limited role in evaluating the nature of renal tumors. In the past, this method was mainly used to diagnose patients with lymphoma or metastases, infectious disease, or tumors with surgical risk.
In recent years, rapid advances in imaging, interventional radiology and cytology techniques have allowed percutaneous renal biopsy to play a greater role in the evaluation of renal tumors in adults. The purpose of this review is to systematically review these advances and the reasons why biopsy plays an important role in the diagnosis of renal tumors. We will describe the experience with percutaneous renal biopsy, technical factors, and the role and limits of the procedure.
Factors for the increased role of biopsy
Percutaneous renal puncture biopsy has become an indication for surgery in more patients based on the following factors: First, advanced imaging evidence such as ultrasound, CT, and MRI can detect more renal tumors, resulting in an increased incidence of renal cell carcinoma and a corresponding increase in the odds of detecting benign renal tumors. Parenchymal masses are determined by using thin-section CT and MRI to reflect the enhancement of the masses. After excluding infectious diseases and malformations, the majority of adult renal tumors are renal cell carcinomas.
However, there is still a proportion of solid masses that are benign, with one report finding 12.8% of 2770 nephrectomies to be benign. By size stratification, 25% of masses less than 3 cm were found to be benign and 44% of those less than 1 cm were benign. Thus, the size of the mass is directly related to its malignancy. Benign masses included verrucous cell tumors (70%), malignant adenomas (18%) and papillary adenomas (4%) and metanephric adenomas (1%). Thus, the second factor is the high percentage of benign renal small solid tumors and the inability to identify their benign or malignant nature by imaging findings alone.
Several studies have identified some diagnostic features that can be used as clues for the diagnosis of benign masses. Homogeneous enhancement and dense masses are considered to be benign malformations containing less fat. However, in general, imaging findings do not distinguish between benign and malignant tumors. For these masses lacking indications for surgical resection, diagnostic options are limited to follow-up and percutaneous biopsy.
In fact biopsy has only recently been applied to identify the nature of benign masses. In this study, 27 patients diagnosed with renal cell carcinoma after enhanced CT or MRI and proposed for percutaneous ablation resulted in 10 masses that were benign. Three of them were oligometastatic malformations. The study suggests that not all of the small solid masses are malignant.
Diagnostic efficiency
Percutaneous renal biopsy in the early days was mainly guided puncture under fluoroscopy, and then CT and ultrasound-guided techniques were gradually applied to puncture biopsy of abdominal (including renal) masses. The results of these studies confirm the ease and safety of this procedure in determining the nature of masses. In fact, many investigators have confirmed the value of percutaneous biopsy in the qualitative diagnosis of abdominal masses as an effective tool to obtain a histological diagnosis. In addition, the cost of percutaneous biopsy is low compared to surgical biopsy.
Since then, several researchers have focused on the clinical use of percutaneous biopsy in renal masses and have improved the effectiveness and usefulness of the procedure. Many findings have been published in radiology, pathology, and urology journals. One study reported that renal mass biopsy changed the treatment plan for 41% of patients. Biopsy can be used to diagnose many tumors, including malignant and benign lesions.
Malignant tumors
renal cell carcinoma, metastatic cell carcinoma, lymphoma and metastases can be correctly diagnosed by fine needle percutaneous biopsy. In a multicenter study, 261 masses were taken for biopsy and 11% of the masses were metastases. To a large extent, this is attributable to developments in cytology, immunohistochemistry, and cytogenetics. The cytomorphological features, immunohistochemistry and cytogenetic characteristics of various renal tumors have been elaborated.
Several studies have evaluated the sensitivity, specificity and overall correctness of percutaneous biopsy. The results of these studies vary relatively widely due to differences in patient populations, tumor types, guidance tools, and puncture needle sizes. Overall, the sensitivity of percutaneous biopsy in the diagnosis of malignancy is 80-90% and does not take into account the influence of factors such as puncture needle size or whether the specimen is tested by cytology or histology. False negative results mostly occur when the needle is not correctly positioned within the tumor when puncturing a small mass or when the tissue is sampled in a necrotic area of the tumor. False-negative results often occur even with experienced operators, and it is therefore recommended that the nature of the mass suspected to be malignant on imaging should be carefully considered at this time. In one study, after biopsy of 25 small masses (<5 cm), 36% of suspected or atypical cells were sampled. In an abdominal mass biopsy study, 71% of these specimens with atypical cells were malignant. For more useful clinical value, the biopsy report should be as definitive in diagnosis as possible. The absence of malignant cells in a biopsy specimen does not infer that the tumor is benign, and the presence of suspicious or atypical cells does not infer that the tumor is malignant.
Specificity is 83%-100%, and false-positive diagnosis of malignancy is rare, although there have been reports of misdiagnosis of a calcified cyst, multifocal cystic nephroma, vascular smooth muscle lipoma, and chronic pyelonephritis as malignancy. It is important to note that most of these publications were published in 1990 or earlier, so we believe that these results do not reflect current cytologic examination capabilities. In one study the use of a fine needle of 0.8 mm was found to reduce false positive results, but finer needles had a higher sensitivity.
Among the patient-related factors affecting biopsy results, the most important one is the size of the mass. In fact, masses smaller than 3 cm have lower biopsy sensitivity than large masses, and small masses are more difficult to reach the target.
Determination of renal tumor subtype and grading
In addition to proper diagnosis of renal tumors, clinical evaluation of tumor subtype and grading is more important. Determining the subtype and grade of the cancer not only helps determine the patient’s prognosis, but also allows the physician to select the appropriate treatment. This is especially important for patients undergoing partial nephrectomy or percutaneous ablation. In a controlled study of fine needle aspiration biopsy specimens from 38 primary tumors and final postoperative specimens, 74% of 34 tumors were correctly identified preoperatively for their subtype, including 15 clear cell carcinomas, 4 papillary carcinomas, 4 verrucous cell tumor s, and 2 suspicious cell carcinomas. 2 sarcomatoid renal cell carcinomas and 3 papillary renal carcinomas were misclassified as clear cell carcinomas.
Sarcomatoid renal cell carcinoma, which accounts for approximately 5% of all kidney cancers, has a worse prognosis than all other subtypes, making correct diagnosis important. Although this type of kidney cancer can be identified on percutaneous biopsy, the reliability of biopsy remains uncertain. We believe that the application of percutaneous biopsy to identify tumor subtypes is promising, but more studies are needed to confirm its correctness, especially for the very rare tumor subtypes.
As for tumor grading, some authors have reported the concordance of fuhrman nuclear grading of biopsy and surgical specimens. fuhrman nuclear grading system is the standard for grading renal cell carcinoma. The tumor is classified into grades 1-4 according to the nuclear characteristics of the cells, and the more nuclei and enlarged nuclei, the higher the grade.
A large puncture needle can increase the chance of determining the subtype and grade of renal cell carcinoma. neuzillet et al. reported that a total of 88 small (<4 cm) renal solid masses were detected using a ct-guided 18-gauge fine needle, and 92% of the tumor tissue types were correctly identified, but the correct fuhrman nuclear grading rate was only 69.8%.
Benign tumors
Although a high rate of correct biopsy of renal masses has been reported in the literature, most data are from patients with renal cancer. No large case reports of benign renal tumors have emerged. In fact, most benign tumors can be diagnosed on the basis of imaging without the need for renal biopsy. Therefore the sensitivity and specificity of fine needle aspiration biopsy for the diagnosis of benign tumors is not known. However, benign masses can also be diagnosed using percutaneous biopsy. neuzillet et al. reported 14 benign tumors diagnosed by biopsy, of which 10 were adenomas, 3 were malformations, and one was a cystic nephroma. Only 5% of the samples could not be ultimately characterized. The authors concluded that percutaneous biopsy could be used to diagnose benign solid tumors, thus avoiding surgical measures.
In another study, 106 masses were biopsied using an 18-g fine needle and malignancy was correctly diagnosed in 91, however, in 1/3 of the 15 benign tumors, they were incorrectly diagnosed. The authors concluded that intraoperative biopsies need not be used to guide surgical decisions. The biopsy specimens in this study were frozen sections, he stained for rapid diagnosis. Therefore, its results are not useful for the evaluation of percutaneous biopsy. More sophisticated cytologic evaluation of percutaneous biopsies, including smear, cell block sections, and immunohistochemical staining, was used. In a subsequent study, the group applied 18g fine needle biopsy intraoperatively to 100 surgically resected specimens, 85% of which were malignant, and the authors reasoned that percutaneous biopsy could not be recommended preoperatively for renal tumors because of its low specificity. However, if they use cytomorphological evaluation in combination with other complementary diagnostic methods such as immunohistochemistry and cytogenetics, its specificity should be higher.
Vascular smooth muscle lipoma
Vascular smooth muscle lipoma is one of the most common benign renal tumors and can often be diagnosed by imaging. However, sometimes a renal biopsy is required to make the diagnosis, especially in those with fat-depleted vascular smooth muscle lipomas.
Renal biopsy was once thought to have a limited role in the diagnosis of vascular smooth muscle lipomas, especially when fine needle aspiration was used, because these benign masses can exhibit features such as nuclear heterogeneity and pleomorphism and can easily be misdiagnosed as malignant tumors. Currently, the differential diagnosis of vascular smooth muscle lipoma and renal cell carcinoma is often made with the help of immunohistochemical methods. The melanin-associated protein hmb-45 is frequently expressed in vascular smooth muscle lipomas, but not in renal cell carcinomas or sarcomas. Vascular smooth muscle lipomas do not contain cytokeratin, a marker that is often expressed in renal carcinomas. The sensitivity and specificity of these markers can reduce the concern of those who hold the skeptical view that a puncture biopsy of a suspected renal vascular smooth muscle lipoma could be misdiagnosed as renal cancer.
Because renal vascular smooth muscle lipomas are blood-rich tumors that are prone to spontaneous bleeding when large in size, there is often a concern that bleeding will occur after renal biopsy. However, in our experience and in the literature, bleeding after puncture biopsy of vascular smooth muscle lipoma is not more common or more severe than that of other renal tumors, especially when fine needle puncture is used.
Neoplastic cell tumors
The role of percutaneous renal biopsy in the diagnosis of oncocytomas is still controversial. The value of the diagnosis of these tumors is to determine that the tumor is benign and thus avoid surgical intervention. Imaging features include the presence of a scar in the center of the uniformly enhancing tumor and the “spoke-wheel” sign on angiography, but these signs are not present in this lesion and are often seen in renal cell carcinoma.
Renal biopsy was also considered to have a limited role in the diagnosis of oncocytoma for the following reasons. Neoplastic cells can be found in a variety of renal tumors, including nephroblastoma and neoplastic renal cell carcinoma, i.e., some renal cell carcinomas that are often considered to be of low metastatic potential, including granulosa cell carcinoma, suspicious cell carcinoma, and eosinophilic papillary renal cell carcinoma. Although conventional renal biopsies do not confirm the diagnosis of oncocytoma, a mass containing oncocytes can be diagnosed, and oncocytoma can be diagnosed based on histochemical, immunohistochemical, and ultrastructural studies.
A retrospective controlled study of fine needle aspiration specimens and postoperative specimens from 19 oncocytic adenomas found that although there was a large overlap in tumor cytology type between the two, immunohistochemical methods could be used to differentiate oncocytoma from oncocytic renal cell carcinoma. The vimentin protein was expressed negatively in all oncocytomas and positively in granulosa cell carcinoma and eosinophilic papillary renal cell carcinoma. In contrast, suspensory cell carcinoma can be differentiated from oncocytoma based on hale colloidal iron staining results. The former is widely present within the tumor, whereas it is not expressed or is limited in oncocytoma.
Although the current research progress is encouraging, it cannot be inferred from the limited findings that renal puncture biopsy can reliably diagnose oncocytoma. However, based on the results of these studies it can be assumed that renal biopsy can definitely diagnose neoplasms of oncocytoma, sometimes, based on some characteristic morphological changes and negative hale colloidal iron staining.
Other tumors DDD metanephric adenoma, a rare tumor, can be diagnosed based on renal biopsy results. Smooth muscle tumor, also a rare tumor, is difficult to diagnose by percutaneous biopsy because it is differentiated from smooth muscle sarcoma based on the biopsy specimen. Renal adenoma is a small tumor that is difficult to differentiate from low-grade papillary renal carcinoma, except for the difference in size. Sometimes this tumor is so small that it is difficult to successfully find the target. In fact, most are also difficult to detect by imaging.
Technical considerations
The technical approach to image-guided renal mass biopsy is the same as for other abdominal puncture biopsies. Because this review focuses on the role of renal biopsy in the evaluation of tumors, only technical factors related to its efficiency and safety are discussed here. In fact, efficiency and safety are the result of a combination of many factors, such as patient cooperation, tumor type, tumor size, and operator experience. Among them, image guidance equipment and puncture needle size are the most important technical factors that affect efficiency and safety.
Currently, the most common guidance devices used for percutaneous biopsy are ct or us, and mri is rarely used. to our knowledge, no studies have shown that one guidance device can be used for all tumor biopsies. us can be used at the bedside and is the most widely used. real-time, multiplanar viewing, no radiation loss, and low cost are all advantages over ct or mri. However, not all renal masses can be visualized at the us. The bowel and pleural cavity in the puncture route are difficult to visualize and therefore the location of the needle is difficult to visualize. ct can visualize almost all renal masses (sometimes requiring contrast enhancement) and can visualize the bowel, pleural cavity and puncture needle extremely well. mri is mainly used for rare masses that are difficult to visualize with ct and us. In general, we recommend using the imaging device that best displays the mass and is most familiar to the operator.
Percutaneous renal biopsies can be performed with a variety of different sized puncture needles. For the purpose of obtaining tissue for diagnosis, puncture needles include fine needles (20 g or smaller) or slightly larger needles (19 g or larger), and 18 g needles have also been used. Although the size of the puncture needle is somewhat related to the success and safety of the procedure, we prefer to think that all operative procedures are related to it. In general, tissue specimens obtained with fine needles are used for cytologic analysis, whereas specimens obtained with coarse needle biopsies are used for histologic analysis. There is no evidence yet to suggest which sampling method is superior.
The diagnostic sensitivity of percutaneous biopsy using only fine needle puncture is 75-95%. Other investigators have had even lower results. We believe that their results are more likely due to mis-targeting of the puncture rather than the size of the puncture needle. Some studies have shown similar diagnostic sensitivity using both fine and coarse needles (18 g), with a sensitivity of 76%-93% for detecting malignant tumors. Because these studies used both fine and coarse needle biopsies, it is difficult to distinguish the relative sensitivity values of 18g puncture needles.
lechevallier et al. evaluated biopsy specimens with an 18-g puncture needle and ct guidance and found results similar to those obtained with the combination of fine and coarse needles, including a 21% failure rate, 8% requiring repeat biopsies, and an overall correct rate of 89%. rybicki et al. biopsied 115 masses with both fine and coarse needles and had a sensitivity of 90%, however, the use of a puncture needle coarser than 20 g 23 biopsy specimens showed no false negative results, and the results suggest that coarse needles can improve biopsy efficiency.
The present findings suggest that fine needle aspiration biopsy is appropriate for sampling most renal masses and that coarse needles can be used in certain circumstances. Although the coarse needle can increase the rate of correct diagnosis, it also increases the chance of complications. In clinical practice, fine needle aspiration can be used first to obtain specimens, and intraoperative cytologic analysis can be performed on one or two specimens; if the cytologic results are more positive, the procedure is then concluded, and if in doubt, histologic analysis is performed using coarse needle sampling.
Complications
Percutaneous renal mass biopsy is a safe method. Bleeding is the most common complication, but is usually asymptomatic clinically, detected only on postoperative CT scans, and is self-limiting. In one study, ct scans of 200 post-biopsy patients revealed perirenal hematomas in 91%. Major bleeding requiring blood transfusion is rare. Hematuria can be present, mostly presenting as microscopic hematuria, while sarcoid hematuria is rare, accounting for about 5-7% of cases. Carnal hematuria is most likely due to inadvertent manipulation or biopsy into normal renal tissue. Most of them are also self-limiting but can persist if an arteriovenous fistula develops.
In general, the thicker the puncture needle, the higher the chance of bleeding complications. In a study of 203 renal mass biopsies, 1.5% of procedures required blood transfusions. Thicker puncture needles also increase the risk of pseudoaneurysm, and its clinical symptoms can not appear until months after surgery. caoili et al. reported a case of intrarenal pseudoaneurysm 3 months after surgery. This complication can be treated with arterial embolization.
Pneumothorax can also occasionally occur, and this risk can be avoided by using a subanterior border route. If the intercostal route is used, the incidence of pneumothorax remains low as long as the lung tissue is not penetrated.
Tumor implant dissemination via the puncture route is one of the consequences of percutaneous biopsy, but it occurs rarely, less than 0.01%. We believe that the reason for the occurrence of implantation is more likely to lie in the subtype of the tumor. Some authors believe that metastatic implants are more likely to occur in metastatic metastases of metastatic cells and suggest that percutaneous biopsy should not be performed if this tumor is suspected. The relationship between the risk of implantation and the size of the puncture needle is not well understood. In general, because penetrating channel dissemination rarely occurs, this concern should not be considered a contraindication to surgery when there is a clear indication for surgery, and biopsy can still be performed even in metastatic cell carcinoma, as long as the diagnosis is not clear.
Surgical indications of percutaneous biopsy
1. Definite surgical indications
(1) Clear history of extra-renal primary tumor in patients with DDD This is one of the most common surgical indications for percutaneous biopsy of renal masses, i.e. patients with masses in the kidney and extra-renal primary malignant tumors. Percutaneous biopsy helps to identify surgically resectable renal cell carcinoma and renal metastases. This pretreatment confirmation is necessary because all metastases ultimately require medical treatment, whereas renal cell carcinoma relies on surgical treatment. Biopsy has a sensitivity of 90%. This diagnosis is even more critical in patients with lymphoma and lung cancer, as these two tumors more commonly spread to the kidney. In one study, these tumors were found to be confirmed as renal cell carcinoma in half of the patients despite the possibility of metastasis to the kidney. Therefore, patients with an extrarenal primary malignancy presenting with a renal tumor are not always metastatic and a renal biopsy should be performed at this time. Generally, imaging features are difficult to identify renal cell carcinoma and metastases alone, however, cystic renal masses are rarely metastases.
(2) Kidney cancer that is difficult to be removed surgically
Percutaneous renal biopsy is also commonly used for renal tumors that are considered inoperable on imaging findings. Biopsy can be used to obtain information for histologic diagnosis, selection of treatment options, and to rule out the need for surgical treatment. In patients who have extrarenal tumors in addition to the renal tumor, biopsy of the renal mass may be less lethal than biopsy of the extrarenal mass. For example, if a patient has a lung tumor and a renal mass, a biopsy of the kidney may prevent the occurrence of pneumothorax.
(3) Patients with compound lesions
Percutaneous biopsy can also be used for patients with resectable renal cell carcinoma, but the presence of compound lesions in the patient increases the patient’s surgical risk. Examples include heart and lung disease, solitary kidney, and renal insufficiency. Preoperative diagnosis can better evaluate the risk and benefit degree of surgery.
(4) Patients with renal masses that may be due to infection
Focal bacterial pyelonephritis sometimes presents with mass-like features, similar to a renal tumor, and therefore, a correct diagnosis can prevent unnecessary surgical execution. Although most infectious renal diseases can be diagnosed clinically, renal biopsy can help to establish the diagnosis of renal tumor or to identify the cause of infection.
2. Emerging surgical indications
(1) Small intrarenal dense, homogeneously enhancing masses DDD As mentioned above, dense (relative to the renal parenchyma), homogeneously enhancing renal tumors <3 cm in diameter may be benign, such as oligo- or non-fatty vascular smooth muscle lipomas (about 5%). In one study, of 175 resected solid tumors, 6 (3%) were oligofatty vascular smooth muscle lipomas, all of which were dense and homogeneously enhancing, and only 2% of renal cell carcinomas exhibited this feature. Therefore, when a similar mass is encountered, it is reasonable to assume that the tumor is benign and should be evaluated further rather than assuming it is renal cell carcinoma and treating it directly with surgery.
MRI can help to differentiate renal cell carcinoma from oligohyalingoid vascular smooth muscle lipoma, which shows low signal on t2-weighted images at mri, and the pathologic basis may be that the tumor contains smooth muscle cells. Clear cell carcinoma shows high signal on tx images, so if a renal mass that enhances to high signal shows high signal on t2 images, it is likely to be renal clear cell carcinoma. However, papillary renal cell carcinoma can also be low-signal on t2 images, and the pathology may be based on the presence of iron-containing heme in the cytoplasm of the tumor. Therefore, if a renal tumor that enhances with high signal shows low signal at t2, it should be considered to be either an oligophilic vascular smooth muscle lipoma or a papillary renal cell carcinoma. The only way to distinguish between these two tumors is by renal aspiration biopsy. A dense homogeneous enhancing mass can also be other benign masses such as adenoma, verrucous adenoma and smooth muscle tumor.
(2) Patients with renal tumors proposed for percutaneous renal ablation
Because small renal tumors may be benign, percutaneous biopsy should be performed if the imaging findings are inconclusive as to the benignity or malignancy. Histologic diagnosis is obtained prior to ablation for two reasons, one of which is that percutaneous tumor ablation is still limited to the field of study by many. Percutaneous tumor ablation, including cryotherapy and radiofrequency ablation, is considered an alternative to partial nephrectomy for small renal cell carcinoma. These techniques can achieve comparable efficacy to partial nephrectomy. However, in contrast to surgical resection (where the entire tumor can be examined pathologically), percutaneous techniques rely only on imaging and biopsy findings for diagnosis.
Many studies of renal tumor ablation have included cases in which the diagnosis of renal cancer was based on imaging findings alone. In cases where benign masses are present and misdiagnosed as renal cancer, the treatment outcome is likely to be overestimated. Therefore, we believe that a correct diagnosis before surgery is important.
Secondly, we believe it is also prudent to obtain a histological diagnosis before ablation to avoid the potential risks associated with ablation if the patient has a benign mass. Biopsy also helps to prevent patients with benign tumors from receiving an incorrect cancer diagnosis, thus avoiding unnecessary imaging follow-up and clinical follow-up.
Since renal ablation is mainly applied to small masses less than 3 cm in diameter, biopsy results are sometimes not conclusive. In fact, tuncali et al. found that the biopsy results were inconclusive in 7 of 17 patients with masses considered malignant. Also, the biopsy diagnosis of benign tumor was not a definitive result.
(3) Indeterminate cystic renal tumors
The value of percutaneous biopsy for the evaluation of indeterminate cystic renal tumors is not certain, and although biopsy of this mass has been performed for many years, we have designated this indication as one of the emerging indications because a recent study has led us to consider its greater role. These are cystic masses with typical features including multiple septa, thick diaphragm, thick walls and indeterminate calcifications.
The mass is also considered a surgical mass because it may be malignant or diagnosed as benign when imaging is not certain or only after surgical resection. This last factor is also the main reason why biopsy is considered to have its limited value.
Benign indeterminate cystic masses are usually complex cysts with an inflammatory response. Therefore biopsy specimens obtained from the cyst wall or cyst contents include only renal endothelial cells, inflammatory cells and fibrous tissue. However, these materials cannot be used to diagnose a cyst as benign. Failure to find malignant cells may still be an incorrect sampling or a missed test.
Because of the limited role of biopsy in indeterminate cystic masses, direct surgical measures are often performed clinically without biopsy. However, the incidence of malignant masses in their postoperative specimens varies from 31% to 100%. Although surgery ensures that kidney cancer is not missed, as many as 69% of patients undergo unnecessary surgery. Recently, some scholars have affirmed the role of percutaneous biopsy in identifying benign cystic renal tumors. In one study, 199 indeterminate cystic tumors underwent mass biopsy with a positive diagnosis of 88%.
The biggest problem in biopsy of cystic renal tumors is the difficulty in confirming a negative result, and in most studies it is considered benign simply by follow-up if the mass does not grow within 1 year. However, the time interval for determining a benign mass remains unclear, and indeed, some small solid malignant tumors grow very slowly or do not grow at all.
Future research directions
Because the cause of renal biopsy failure is usually the inability to reach the mass target correctly, improving the targeting success of biopsies is essential. With the development of ultrasound, CT and MRI imaging equipment, more advanced targeting techniques continue to emerge, allowing more characteristic tissue specimens to be obtained. Moreover, the continuous development of immunohistochemical techniques, the constant updating of molecular probes and the emergence of new cytological markers have strongly improved the correct diagnosis rate.
The ultimate goal of medicine is to correctly diagnose the nature of renal tumors through advances in imaging techniques without relying on renal biopsy, but until that day arrives, renal biopsy will continue to play an important role in the clinical diagnosis of renal tumors.